Thermite reactions are well characterized and have been used for a variety of applications, including demilitarization of expended ordnance, quick repair welding of railroad tracks, and cutting applications using lances or burning bars. The thermite reaction is an exothermic reaction that can produce temperatures of more than 4,000° F. These temperatures are well above the melting point of most metals. Boosting the rate of the thermite reaction by flowing a stream of oxygen through the materials can raise the reaction temperature from the normal 4,000° F. to the range of 10,000° F. to 16,000° F. Boosting the temperature to this level greatly reduces the time associated with cutting through a material. In addition, directing the burning particles and gases into a jet through a nozzle allows improved removal of molten metal and deeper penetration into the material.
Until this time, one-shot thermite-based devices have been used primarily to make point like, circular holes in materials. Sustained thermite cutting technologies, such as burning bars, achieve linear-shaped cuts by expanding on the initial penetrated area and moving away from the initial point of penetration in a line (similar to a conventional cutting torch). By configuring a single-use apparatus and its associated nozzle into a linear or curvilinear arrangement, the shape of the penetration would be lengthened dramatically. Connecting segments of these devices into a desired shape would allow users to determine the dimensions of a breach area or linear cut.
This thermite-based method will allow operators to penetrate a material in timeframes similar to explosive shape charges without the safety concerns and security risks associated with explosives. In addition, the sustained duration of a thermite jet will more effectively handle discontinuities and interfaces that normally disrupt and dissipate explosively driven shape charge jets. When a linear shaped charge is used for cutting steel on a steel bridge demolition project, a large degree of preparation work must be undertaken to ensure a successful cut or penetration. A “preconditioning” process involves removing overlapped plates and areas of reinforcement with a conventional cutting torch. This process is time consuming, expensive, and dangerous. Conversely, the sustained jet of a thermite charge offers improved performance over multi-plate materials with limited or substantially no preconditioning. The thermite charge's sustained jet also affords a greater assurance in cutting plates of varying thickness, layered plate configurations, and any supporting or reinforcing members that may exist in the middle or on the backside of a material. While the projected thermite charge particle stream is a slower reaction than that of an explosively driven jet, it is very fast from the perspective of the operator. The anticipated timing for material penetration is typically on the order of hundreds of milliseconds.